A One‐sided Highly Relativistic Jet from Cygnus X‐3

Very Long Baseline Array images of the X-ray binary Cygnus X-3 were obtained 2, 4, and 7 days after the peak of a 10 Jy flare on 1997 February 4. The first two images show a curved one-sided jet, and the third shows a scatter-broadened disk, presumably at the position of the core. The jet curvature changes from the first to the second epoch, which strongly suggests a precessing jet. The ratio of the flux density in the approaching jet to that in the (undetected) receding jet is ≳330; if this asymmetry is due to Doppler boosting, the implied jet speed is ≳0.81 c . Precessing-jet model fits, together with the assumption that the jet is intrinsically symmetric and was ejected during or after the major flare, yield the following constraints: the jet inclination to the line of sight must be ≲14°, the cone opening angle must be ≲12°, and the precession period must be ≳60 days.